Metamorphic rocks from the north-eastern part of the Ereendavaa terrane (Eastern Mongolia) :

Altanbaatar Battushig,Demberel Orolmaa,Guo Lei,Jargalsaikhan Tumendelger,Li Pengfei,Orosoo Baatarchuluun,Ren Zhongyuan,Tong Ying,Tserendash Narantsetseg,Tuya Idermunkh,Wang Tao,Yuan Chao,Zhang Le

doi:10.5564/mgs.v26i52.1079

Abstract

In this paper, we have conducted geochronological and geochemical studies on the metamorphic rocks of the Khaychingol and Ereendavaa Formations in the Mogoitiin Gol, Khaychin Gol and Emgentiin Bulag areas from the Ereendavaa terrane and these rocks have been considered to be Precambrian in age. However, new LA–ICP–MS zircon U–Pb dating results indicate that the protolith of the studied metamorphic rocks was formed in two stages: 1) during ~ 296 - 285 Ma, the protolith of mafic, felsic and black schists formed; 2) during ~276 - 271 Ma, the protolith of gneiss and psammitic schists began to deposit. The Early Permian bimodal association composed of low-K basalt and comagmatic high-Na, low-K dacite with high-K calc-alkaline rhyolite, represent protolith of the mafic and felsic schists which were formed in back-arc basin environment. The Middle Permian gneiss, and psammitic schists with sedimentary protolith have geochemical signatures of island arc rocks, such as enrichment of LILE relative to HFSE, and markedly negative Nb, Ta and Ti anomalies, suggesting that they were formed in a continental arc environment. Considering a close spatial relationship of the Ereendavaa terrane with the Mongol-Okhotsk Belt in the north-west, we propose that accompanied with the emplacement of arc magmatic rocks, the arc rifting occurred and formed the Early Permian bimodal volcanic rocks. In the Late Permian, after the formation of the back-arc basin, deposition of the immature deposits as wacke, arkose and litharenite dominated sediments in a continental arc environment started.

Highlights

IntroductionMongolia lies in the central part of the Central Asian Orogenic Belt (Mossakovsky et al, 1994; Zorin, 1999; Badarch et al, 2002; Khain et al, 2003; Jahn, 2004; Windley et al, 2007; Xiao et al, 2010), or Altaids (Sengör et al, 1993; Sengör and Natal’in, 1996), which is fringed by the Siberian Craton in the north and the Tarim and Sino-Korean (North China) Cratons in the south (Fig. 1a), and contains several continental massifs/blocks that are separated by fold belts (Tomurtogoo, 2014)
Zircon U–Pb geochronology Six representative samples of gneiss, schist and schistose sandstone considered typical for Khaychingol and Ereendavaa Formations were selected for LA-inductively coupled plasma-mass spectrometry (ICP-MS) U-Pb zircon dating
Based on new geochronological and geochemical analysis of the studied metamorphic rocks, we can draw the following conclusions: New LA–ICP–MS zircon U–Pb dating results indicate that the protolith of the metamorphic rocks from the north-eastern part of the Ereendavaa terrane were formed in two stages: 1) ~ 296 - 285 Ma, forming of protoliths of mafic, felsic and black schists, which were previously believed to be Mesoproterozoic or Neoproterozoic in age; 2) ~276 - 271 Ma, deposition of protolith of gneiss and psammitic schists, which were believed before to be Paleoproterozoic and Mesoproterozoic in age

Summary

Introduction

Mongolia lies in the central part of the Central Asian Orogenic Belt (Mossakovsky et al, 1994; Zorin, 1999; Badarch et al, 2002; Khain et al, 2003; Jahn, 2004; Windley et al, 2007; Xiao et al, 2010), or Altaids (Sengör et al, 1993; Sengör and Natal’in, 1996), which is fringed by the Siberian Craton in the north and the Tarim and Sino-Korean (North China) Cratons in the south (Fig. 1a), and contains several continental massifs/blocks that are separated by fold belts (Tomurtogoo, 2014). The Ereendavaa terrane is one of the constituent terranes of Kherlen Massif (Fig. 1b), which represents the Mongolian part of the Argun-Idermeg superterrane (Parfenov et al, 2009; Kotov et al, 2013) or so called Central Mongolia-Erguna Belt (Wang et al, 2017). It is widely accepted that the Paleozoic tectonic evolution of the Ereendavaa terrane was dominated by the amalgamation of microcontinental massifs and closure of the Paleo-Asian Ocean, while the Mesozoic evolution was largely influenced by the Mongol -Okhotsk tectonic systems (Dash et al, 2015; Wang et al, 2015; Miao et al, 2016; 2017; 2020; Narantsetseg et al, 2019; Sheldrick et al, 2020).

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